CARDIOVASCULAR IMAGING (K ORDOVAS, SECTION EDITOR)

Contemporary Imaging Findings in Aortic Arch Surgery

Tami J. Bang1,4 • Daniel B. Green1 • T. Brett Reece2 • Dominique DaBreo3 •

Daniel Vargas1

Published online: 7 November 2019

� Springer Science+Business Media, LLC, part of Springer Nature 2019

Abstract

Purpose of Review The purpose of this manuscript is to

review the surgical techniques of aortic arch repair,

imaging techniques for evaluating the pre- and post-oper-

ative aortic arch, and both normal and abnormal post-op-

erative imaging appearances.

Recent Findings Aortic arch repair is a technically chal-

lenging and rapidly evolving procedure, utilizing a variety

of surgical methods that result in variable imaging

appearances. Imaging plays an important role in the diag-

nosis of aortic arch abnormalities, as well as diagnosis of

abnormalities in the adjacent ascending and descending

aorta. Imaging also plays a key role in post-operative

evaluation and surveillance.

Summary Familiarity with aortic arch surgical procedures

and their expected post-operative imaging appearances is

crucial for the radiologist to identify the surgery performed,

recognize surgical complications, and avoid imaging pit-

falls that may be mistaken for complications.

Keywords Aortic arch repair � Hybrid aortic repair �Elephant trunk � Frozen elephant trunk

Introduction

Aortic arch repair is an evolving field, with relatively loose

guidelines on indications and limited literature on imaging

appearance and surgical techniques. Whether a partial or

complete repair, aortic arch surgery is technically chal-

lenging, requiring interruption of cerebral and systemic

circulation [1••]. Supportive techniques include cardiopul-

monary bypass and hypothermic circulatory arrest with

cerebral protective adjuncts; these are employed to safely

manipulate the arch vessels [1••]. Imaging plays a key role

in diagnosis and pre-operative planning for aortic arch

disease, as well as post-operative surveillance. Further-

more, imaging is required if management of the adjacent

aorta is planned. The purpose of this manuscript is to

review the indications and surgical techniques for aortic

arch surgery, imaging techniques for evaluation of the pre-

and post-operative aortic arch, and potential operative

complications and imaging pitfalls.

Indications for Intervention of the Aortic Arch

Surgical Intervention

Aneurysm is a common indication for aortic repair, defined

as dilatation of the aorta greater than 50% beyond its

normal diameter [1••]. Isolated aortic arch aneurysms are

This article is part of the Topical collection on Cardiovascular

Imaging.

& Tami J. Bang

Tami.Bang@cuanschutz.edu

1 Division of Cardiothoracic Imaging, Department of

Radiology, University of Colorado – Anschutz Medical

Campus, Aurora, CO, USA

2 Division of Cardiothoracic Surgery, Department of Surgery,

University of Colorado – Anschutz Medical Campus, Aurora,

CO, USA

3 Division of Cardiothoracic Radiology, Department of

Diagnostic Radiology, Queen’s University School of

Medicine, Kingston, ON, Canada

4 University of Colorado – Anschutz Medical Campus,

Mail Stop L954, Leprino Building, 12401 E 17th Avenue,

Room 516, Aurora, CO 80045, USA

123

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https://doi.org/10.1007/s40134-019-0343-7

rare, accounting for approximately 10% of aortic disease

[2••, 3]. Guidelines for aortic arch intervention are less well

defined than those of other aortic segments [1••]; in addi-

tion, a relative paucity of data on aortic arch pathology,

natural history, and post-operative outcomes has resulted in

less stringent criteria for surgical intervention. Complete

operative aortic arch replacement is indicated when the

entire arch is aneurysmal (greater than 5.5 cm) or if rate of

growth exceeds 0.5 cm/year [1••, 4].

Isolated aortic arch aneurysms are frequently asymp-

tomatic and discovered incidentally [1••], or they may

alternatively cause symptoms related to compression on

other organs (chest pain, dysphagia, hoarseness, recurrent

respiratory infections) [1••]. In these cases, symptomatol-

ogy may supersede the standard measurement thresholds

for intervention [2••]. However, aortic arch abnormalities

commonly occur in conjunction with abnormalities in the

adjacent segments of the aorta, and decisions on arch

surgery are often dictated by disease in the contiguous

aortic segment [2••]. In our practice, ascending aortic

abnormalities may be the primary indication for surgery,

but aortic arch replacement is also performed for con-

comitant arch disease. Additionally, descending aortic

disease may be addressed by creating a landing zone for

endovascular repair.

Acute aortic dissection and intramural hematoma are

classified according to the origin and extent of aorta

involved. The Stanford classification system typically

divides aortic dissections into type A (involving the

ascending aorta) and type B (not involving the ascending

aorta) [2••]. Surgical nomenclature is evolving regarding

aortic arch dissection being classified as type A, type B, or

a separate classification. Type A aortic dissection is con-

sidered a surgical emergency [5]. Type B is typically ini-

tially managed medically, with potential subsequent non-

emergent intervention. However, if the dissected aortic

arch is aneurysmal or if there is extensive arch destruction,

surgical replacement of the entire aortic arch is recom-

mended [2••]. Other details such as location of the dis-

section, size of the dissected aorta, clinical complications,

and patency of the false lumen should be reported to aid in

surgical planning [5]. In our practice, aortic arch repair

may be performed for chronic/residual dissection or

growing aneurysm after type A dissection repair to redirect

flow into the true lumen.

Endovascular Repair

Thoracic endovascular aortic repair (TEVAR), stent-graft

placement has emerged as both an adjunct and alternative

to traditional open surgical aortic repair, primarily in the

straight or tubular portion of the descending thoracic aorta

(DTA). It can avoid the morbidity of a thoracotomy for

open repair, and may also reduce or avoid high-risk

maneuvers such as circulatory arrest and aortic cross-

clamping [2••]. Furthermore, total endovascular repair may

be offered to patients who are poor candidates for tradi-

tional surgical repair [2••].

To define the landing zones for stent-graft placement,

the thoracic aorta has been divided into five zones [1••, 6].

In the Criado classification system (Fig. 1), Zone 0

involves the entire ascending aorta and the origin of the

innominate artery. Zone 1 spans the origin of the left

common carotid artery. Zone 2 spans the origin of the left

subclavian artery, and Zone 3 extends from the origin of

the left subclavian artery to 2 cm down the DTA. Zone 4

extends from the end of Zone 3 through the DTA. This

terminology is also used to describe the location of anas-

tomoses in open or hybrid repair.

Some patients are not considered candidates for

TEVAR. Endograft placement requires 1.5–2 cm of normal

aorta both upstream and downstream of the aneurysm to be

a platform for stent-graft placement [7], acting as a

‘‘landing zone’’ for hardware. In addition, these procedures

require appropriate endovascular access, and extremely

tortuous vessels or severe atherosclerosis may preclude

endovascular approach [2••].

Hybrid aortic repair is a broad term encompassing pro-

cedures that combine endovascular stents and surgical

grafts. A significant advantage of hybrid repair is the

ability to combine a classically staged repair into a single

procedure by addressing multi-segmental aortic disease

with endograft placement [1••]. In addition, it can facilitate

more downstream repair of the DTA or abdominal aorta if

an additional procedure is planned [8]. Hybrid repair is

classified into three types [9]. Type I is performed in iso-

lated aortic arch aneurysm, with debranching of the arch

vessels that are reconstructed on the native ascending aorta.

Type II is performed with ascending aortic graft repair and

stent-graft placement of the aortic arch; the arch vessels are

Fig. 1 Criado classification of thoracic aortic zones for endovascular

repair

32 Page 2 of 10 Curr Radiol Rep (2019) 7:32

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debranched and reconstructed on the ascending graft. Type

III is performed in extensive thoracic disease, with graft

repair of the ascending aorta and aortic arch; the graft

creates a landing zone for endovascular DTA repair and

may require staged repair. Hybrid procedures can be cus-

tomized to each patient, adapting to the segment of aorta

requiring repair, as well as creating appropriate landing

zones for endograft placement.

Surgical Techniques and Imaging Appearanceof Aortic Arch Repair

Hemiarch

Hemiarch (or partial arch) repair is a general term that

describes replacement of the proximal aortic arch. It

involves a variable degree of resection along the lesser

curvature of the aortic arch; the greater curvature is left

intact. Consensus guidelines recommend hemiarch repair

in conjunction with ascending aortic repair when the

aneurysm includes the proximal aortic arch. The beveled

distal margin of the graft is anastomosed to the proximal

aortic arch along the lesser curvature [1••, 10, 11]. The arch

vessels (brachiocephalic, left common carotid, and left

subclavian arteries) are controlled to maintain cerebral

protection but remain in their native position [1••, 10],

avoiding the need for debranching and reimplantation.

In more recent practice, hemiarch repair is frequently

performed in conjunction with emergent ascending aortic

repair for Type A dissection. In these cases, the focus is to

direct as much flow to the true lumen as possible. In theory,

this reduces re-operation rates by decreasing the rate of

downstream and delayed aortic events [11]. This has driven

the use of frozen elephant trunk (discussed below) in the

setting of acute dissection to isolate true lumen flow.

On CT, the distal hemiarch anastomosis appears as an

indentation along the undersurface of the aortic arch with a

beveled margin with the native aorta. The arch vessels

remain attached to the greater curvature of the native aortic

arch (Fig. 2). 3D surface reformats may be helpful in

identification of the distal anastomosis. The proximal

anastomosis has a variable appearance and may be sewn to

the native aortic root, a Valsalva graft, or to a prosthetic

aortic valve (depending on what additional procedures

have been performed). Felt pledgets may be used to rein-

force the anastomosis, aiding in localization of the anas-

tomosis on CT. In our practice, felt pledgets may be

sandwiched on both sides of the anastomosis, buttressed on

the outside of the suture line, or placed into the false lumen

as a neomedia to promote flow into the true lumen.

Total Arch Repair

With extensive aortic arch aneurysm or dissection, a

hemiarch repair is insufficient for the degree of aortic

disease. Complete aortic arch repair is instead required to

treat the mid and distal aortic arch. In all cases of total

aortic arch repair, the arch vessels must be dissected from

the native aorta and re-implanted to the new aortic graft.

The following configurations can be used:

Total Arch with Island Patch

In the island patch repair, the arch vessels are removed en

bloc from the aorta and attached to the graft as an ‘‘island’’

of native aortic tissue. Because the normal architecture of

the arch vessels is preserved, the island patch technique

resembles the normal appearance of the aortic arch on post-

operative imaging.

The primary advantage of this technique is reducing

surgical and circulatory arrest times [1••]. However,

because it involves transferring a portion of diseased native

aortic tissue, there is an increased risk of anastomotic

pseudoaneurysm in the short-term post-operative periods,

and patch aneurysm in the long-term post-operative periods

[1••]. For this reason, the island patch repair is typically

avoided in young patients, particularly those with con-

nective tissue disease [3].

Four-Branched Arch Replacement

This method of arch reconstruction employs a pre-fabri-

cated 4-branched graft. In addition to the three arch vessels,

a fourth side branch is used for cardiopulmonary bypass

[12]. The arch vessels are individually anastomosed to the

Fig. 2 Hemiarch replacement. a Pre-operative imaging demonstrates

dilatation of the aortic root and ascending aorta. b Post-operative 3D

surface reformat demonstrates changes related to hemiarch repair.

The hemiarch is visualized as a beveled anastomosis (straight arrow)

along the lesser curvature of the aortic arch. There is also an

anastomosis between the hemiarch graft and a valve sparing aortic

root repair (curved arrow)

Curr Radiol Rep (2019) 7:32 Page 3 of 10 32

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graft branches. The fourth side branch is ligated at the

completion of the surgery [1••]. Although this is associated

with longer bypass times than the island patch repair, it

allows for complete resection of the native aortic arch.

Total Arch with Y-Graft

The Y-graft was introduced by Spielvogel et al. [13] as an

alternative approach to aortic arch reconstruction with the

goals of decreasing cerebral ischemia, improving

hemostasis, and allowing for complete removal of native

aortic tissue [14]. In this method (also known as the

Spielvogel technique), a branching graft from the aortic

graft creates a platform for individual anastomosis of the

arch vessels (Fig. 3) [1••]. The arch vessels are anasto-

mosed and occluded individually in the reconstruction

process, and during periods of individual vessel occlusion,

the other branches can be perfused.

When possible, a left carotid–subclavian artery trans-

position or bypass is performed prior to sternotomy [4] to

facilitate more proximal arch manipulation at the time of

aortic surgery and improve surgical hemostasis (Fig. 4). A

more proximal anastomosis of the aorta-to-graft (proximal

to the left subclavian origin) avoids injury to the left

recurrent laryngeal nerve and improves surgical hemostasis

[1••, 3]. Alternatively, a fenestration through the graft or

stent graft has also been employed to preserve flow to the

left subclavian artery which would otherwise be covered

[8]. In cases requiring a more proximal aortic repair,

carotid–carotid artery bypass accompanies the left carotid–

subclavian artery bypass [6].

Surgical Techniques and Imaging Appearancefor Combined Aortic Arch and Descending AorticRepair

Classic Elephant Trunk

The classic elephant trunk procedure was first described by

Borst et al. [15] as a staged repair of extensive aortic dis-

ease—the ascending aorta and arch via sternotomy and the

DTA via left thoracotomy [1••, 16••] (Fig. 5). In stage 1,

the ascending aorta and arch are repaired and anastomosed

to the distal arch with a free-floating portion of the graft

(termed the elephant trunk) left suspended within the

proximal DTA [1••]. In the setting of aortic dissection, the

dissection flap is resected and fenestrated as far down into

the DTA as possible to open the true lumen. On CTA, the

free-floating elephant trunk appears as a flap-like structure,

with contrast on both sides, mimicking a residual aortic

dissection. Radiopaque markers may be placed along the

elephant graft to facilitate stage 2. Careful correlation with

surgical history is necessary for accurate identification of

expected post-operative findings.

The classic open elephant trunk repair is associated with

several inherent risks. In most cases, patients are allowed to

recover between stages for a 4–8 weeks interval [1••].

During this period, patients remain at risk for dissection,

pseudoaneurysm, or rupture of the native descending aorta;

up to 25% of patients do not survive to the second stage

[9]. In addition, the inherent risks associated with a second

Fig. 3 Trifurcated Y-graft of the aortic arch with frozen elephant

trunk repair. a Axial CT images from a gated CTA demonstrates an

acute Stanford Type A dissection. There is a dissection flap with

intimal defect in the ascending aorta and descending aorta (straight

arrows). The dissection flap also involves the aortic arch (not included

on the field of view). b Follow-up imaging after frozen elephant trunk

repair. A branching tri-furcating Y-graft (straight arrow) has been

anastomosed to the ascending aortic graft, supplying the right

brachiocephalic, left common carotid, and left subclavian arteries.

A stent graft has been placed in the true lumen of the descending aorta

(curved arrow). Note the residual dissection in the downstream

descending aorta (arrowhead)

Fig. 4 Zone 2 repair with subclavian revascularization. 3D surface

reformat demonstrates post-surgical changes from aortic arch

replacement and frozen elephant trunk repair. A carotid–subclavian

transposition (curved arrow) was performed, allowing for a more

proximal placement of the stent graft (straight arrow). Incidentally, a

saphenous vein graft is present (arrowhead)

32 Page 4 of 10 Curr Radiol Rep (2019) 7:32

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surgical procedure have to be considered in patients with

multiple comorbid conditions.

The elephant trunk then facilitates DTA repair during

the second stage via either left thoracotomy or an

endovascular approach [10]. The elephant trunk graft is

retrieved and extended to replace the DTA. After com-

pletion of both stages of the elephant trunk procedure, the

imaging appearance is identical to graft repair performed

by any open method without evidence of prior elephant

trunk.

Frozen Elephant Trunk

In 1996, the frozen elephant trunk repair was introduced as

an alternative to the classic elephant trunk procedure [17].

This modification allows both aortic arch and proximal

descending aortic repair to be performed in a single pro-

cedure, eliminating the risks of a staged procedure. From a

median sternotomy approach, an endovascular stent graft is

introduced into the distal aortic arch/DTA during

circulatory arrest in an antegrade fashion [1••, 3], utilizing

intravascular ultrasound to identify the true lumen in dis-

section. The proximal aspect of the stent is securely sutured

at the anastomosis, similar to the technique used in a

classic elephant trunk. However, the distal aspect of the

stent graft can be anchored to the DTA, fully excluding the

descending aortic aneurysm and repairing both the aortic

arch and DTA in a single procedure (Fig. 3b) [18]. In the

case of a dissection, placement of a stent graft into the

DTA excludes the false lumen [4]. Another method is to

place a soft surgical graft, followed by a stent graft in a

stepwise fashion.

More recently, a modified frozen elephant trunk tech-

nique has been introduced—the Buffalo trunk repair [1••].

As part of this modification, the stent graft is placed inside

a traditional surgical graft, both are delivered into the true

lumen of the DTA simultaneously. By deploying the stent

graft and soft graft at the same time, this repair is associ-

ated with shorter bypass and circulatory arrest times than a

traditional frozen elephant trunk repair [4]. The post-op-

erative imaging appearance of the frozen elephant trunk

and buffalo trunk repairs are nearly indistinguishable. The

key difference is that in the buffalo trunk repair, the

anastomosis between the graft and the stent graft is rein-

forced with a felt strip along the outer surface of the sur-

gical margin. On CTA, the felt ring creates a hyperdense

demarcation of the anastomosis.

Imaging Techniques of Post-operative Aorta

Cross-sectional imaging of the thoracic aorta is indicated

after aortic dissection or non-emergent repair of the

ascending aorta. In the case of chronic type B dissection or

repaired type A dissection with residual downstream dis-

section, the weakened aorta remains susceptible to ongoing

dilatation. Current guidelines for imaging recommend

follow-up imaging at 1, 3, 6, and 12 months after surgery,

and following this, yearly monitoring for aortic enlarge-

ment [2••]. Guidelines also suggest follow-up with a single

modality for better comparison (e.g., either or CT or MR,

not alternating) [2••].

CT is the mainstay of post-operative evaluation of the

aorta, due to its ready availability and high spatial resolu-

tion. In our practice, we routinely obtain a non-contrast

phase on the first post-operative CT examination. Initial

non-contrast images allow for reliable identification of

hyperdense surgical material [16••], which can be difficult

to differentiate from pseudoaneurysm or leak on post-

contrast images. In addition, this allows for identification

of hyperdense blood products and post-operative hema-

toma, which may also be obscured on post-contrast images

[16••]. If available, dual-energy CT may be used to employ

Fig. 5 Classic elephant trunk repair. a Initial pre-operative CTA

images demonstrates a chronic dissection flap in the aortic arch and

descending aorta (curved arrow). b Illustration for of the elephant

trunk repair after stage I repair. Note the free-floating graft in the

DTA (arrowhead). c Contrast-enhanced CTA images following Stage

1 repair of the ascending aorta and aortic arch. The free-floating

elephant trunk graft is in the descending aorta (straight arrows),

mimicking a dissection flap. d Post-operative MIP reformat images

following stage 2 demonstrates completion of the descending thoracic

aortic replacement. Illustration is reproduced from Fig. 10a in

original publication: Green DB. Mimics of complications in the

post-operative aorta on CT. Radiology: Cardiothoracic Imaging

2019;1(4):e190080. �RSNA, 2019

Curr Radiol Rep (2019) 7:32 Page 5 of 10 32

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ultra-high pitch, low-dose technique or virtual non-contrast

image reconstruction [16••]. In our practice, we obtain non-

contrast images only on the first post-operative imaging

study; subsequent examinations can be performed in the

post-contrast phase only, provided no other surgical inter-

vention has been performed to alter the baseline appear-

ance of the surgical field.

After non-contrast images are obtained, CTA images

should be performed with either ECG gating or ultra-high

pitch technique to reduce artifact related to cardiac motion

in the aortic root or the ascending aorta [1••, 16••]. Retro-

spective gating is favored, as some abnormalities may be

seen only on certain phases of the cardiac cycle [19•]. In

our practice, we routinely use retrospective gating with

dose modulation for CTA evaluation of the aortic root and

ascending aorta. Delayed venous phase images are

obtained to assess for endoleaks after endovascular repair

[16••] and late opacification of the false lumen in residual

dissection. Other complications may be best seen on

venous phase, including inflammatory fat stranding or rim

enhancement related to infection. In our practice, post-

processing techniques such as multiplanar reformats,

maximum intensity reformats, and 3D volume rendering

are typically performed.

MRA can also be used to evaluate the post-operative

aorta. MRA should be performed using ECG gating, to

minimize cardiac motion artifact. As major advantage,

MRA uses no ionizing radiation, and can be used when

iodinated intravenous contrast is contraindicated. MR may

also better differentiate slow flow from true thrombus in

the setting of excluded aneurysm or false lumens [10, 19•].

However, the spatial resolution of MRA is lower than that

of CTA, and images may be degraded by metallic artifacts-

related surgical material or stent grafts.

Post-Operative Imaging

Normal Post-Operative Appearance and Potential

Pitfalls

In the immediate post-operative setting, complex fluid and

gas in the surgical bed can be a normal finding. In addition,

hemostatic material such as Gelfoam� or Surgicel� may

appear as a heterogeneous gas and fluid collection. Medi-

astinal blood products may also be present in the peri-

operative setting. Mild rim enhancement may be a normal

finding, and not necessarily infectious in the immediate

post-operative setting [19•].

Felt pledgets are used for re-inforcement of anastomotic

suture lines. On CT, these are intrinsically dense, and can

mimic a pseudoaneurysm [19•]. Correlation with non-

contrast images and knowledge of typical locations is key

for correct differentiation of surgical material from pseu-

doaneurysm (Fig. 6).

When cardiopulmonary bypass is employed, side-arm

grafts are used to perfuse the systemic circulation after

distal anastomosis is completed. Typically located on the

ascending aorta, innominate artery, or axillary artery, these

branches are divided and tied off near the aortic graft at the

end of surgery. On post-operative imaging, these appear as

small outpouchings of contrast, mimicking a pseudoa-

neurysm (Fig. 7). However, careful correlation with the

surgical history and operative report can help identify these

normal sites of aortic cannulation. In addition, these side-

arm grafts are typically hyperdense and measure approxi-

mately 8 mm in size [16••].

Mild rim enhancement of mediastinal or pericardial fluid

collections may be a normal finding in the immediate post-

operative period, and cannot be reliably distinguished from

low-grade infection [19•]. In these cases, evaluation with

direct fluid aspiration or a tagged white-blood cell scan can

distinguish infection from normal post-operative

enhancement.

Post-Operative Complications

Dehiscence

As described above, consensus guidelines for post-surgical

imaging surveillance is designed to evaluate for both early

and late complications related to aortic repair. In the early

period, complications of aortic surgery include anastomotic

leak/dehiscence and pseudoaneurysm formation. Dehis-

cence is most common in the immediate post-operative

period [19•] and is characterized by contrast material

Fig. 6 Hyperdense felt pledgets. a Contrast-enhanced CTA image

following aortic arch repair. A hyperdense focus along the lateral

aortic arch (straight arrow) is suspicious for a pseudoaneurysm.

b Non-contrast images demonstrate that this is intrinsically hyper-

dense and compatible with a surgical pledget

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external to the aortic lumen (Fig. 8). It most commonly

occurs as a defect in the aorta, such as an anastomosis or

site of bypass cannulation, resulting in contrast extravasa-

tion [19•].

Pseudoaneurysm

A pseudoaneurysm typically occurs at anastomotic suture

lines, appearing as a saccular outpouching of contrast

beyond the expected contours of the aorta on imaging

(Fig. 9) [16••, 19•]. Pseudoaneurysms may also occur at the

site of cardiopulmonary bypass cannulation [16••] or at

sites of infection or abscess formation. On CT, pseudoa-

neurysms are characterized by a communication with the

aortic lumen [19•], contained by a portion of the aorta or

the surrounding tissues. When large, they can compress

adjacent structures such as the airway or pulmonary artery.

Post-operative pseudoaneurysms necessitate prompt re-in-

tervention with open or endovascular repair.

Aneurysm, Dissection of the Native Aorta

Post-operative imaging can prove valuable in the evalua-

tion of the remaining portions of the native aorta. When

aortic repair is performed emergently for dissection, a

residual chronic dissection may be left in the DTA. Post-

operative imaging plays a key role in monitoring the

chronic dissection, evaluating for changes in aortic size or

propagation of the dissection flap.

Even after elective repair for aortic aneurysm, long-term

follow-up on these patients may demonstrate delayed

aneurysm dilatation of the remaining segments of the

native aorta. Indications for re-intervention are the same as

those described earlier, although the patient’s surgical risk

profile should be reassessed. These remaining portions of

native aorta may also undergo aortic dissection (particu-

larly in patients with connective tissue disease), requiring

more urgent intervention [16••].

Fig. 7 Bypass cannulation site. a Post-contrast CTA images demon-

strate a focal hyperdensity along the outer contour of the aortic arch

(arrow) suggesting pseudoaneurysm. b Non-contrast images demon-

strate intrinsic hyperdensity correlating with this area, compatible

with a bypass cannulation site (arrowhead). This is a typical location

for bypass cannulation, and should not be confused with a post-

operative pseudoaneurysm

Fig. 8 Dehiscence following ascending aorta repair with acute type

B aortic dissection. a Axial-gated CTA image demonstrates dehis-

cence along the ascending aorta anastomosis with a focal defect

(straight arrow) and extraluminal contrast (curved arrow). An acute

type B aortic dissection is present in the DTA (arrowhead). b Sagittal

oblique MIP reformat demonstrates the collection of extraluminal

contrast (curved arrow) and acute type B dissection arising distal to

the left subclavian artery

Fig. 9 Post-operative pseudoaneurysm. a Axial CTA image of a

patient following coronary artery bypass grafting. Images demon-

strate a large pseudoaneurysm along the ascending aorta (arrow), with

an associated large mediastinal hematoma (curved arrow). b 3D

surface reformat shows the bi-lobed shape of this pseudoaneurysm,

located along the ascending aorta (arrows). c Due to multiple

comorbid conditions, this patient was not considered a candidate for

re-do sternotomy and open repair. 3D surface reformat after Zone 0

TEVAR demonstrates a new stent graft along the ascending aorta,

upstream of the arch vessels (arrowhead)

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Endoleak and Retrograde Flow

In the setting of a frozen elephant trunk or complete

endovascular aortic repair, a stent graft is secured along an

aneurysmal portion of the aorta. The stent graft is intended

to exclude the diseased aorta and requires an adequate seal

proximally and distally to prevent endoleak—flow from the

aortic lumen into the excluded peri-graft space. Persistent

flow outside of the stent graft is the most common com-

plication after stent-graft deployment [20] and can lead to

progressive aneurysm enlargement and potential rupture

[16••].

Endoleaks are classified into 5 different types, based on

the cause of abnormal blood flow [21]. Type I endoleaks

occur from incomplete attachment at the proximal (IA) or

distal site (IB) of the stent graft (Fig. 10). Type II endo-

leaks occurs from collateral flow into the aneurysm sac. In

the thoracic aorta, type II endoleaks can occur from

intercostal or bronchial collaterals; they can also occur

from the left subclavian artery if carotid–subclavian bypass

has been performed without occlusion of the subclavian

origin. Type III endoleaks occur secondary to structural

failure of the stent graft, and Type IV is due to graft

porosity. Type I and type III endoleaks are seen on CTA

with contrast outside of the endograft on arterial phase.

Delayed images may be necessary or visualization of a type

II endoleak, with slow enhancement of the false lumen or

aneurysm sac from collateral vessels. Type V endoleaks are

characterized by endotension, elevated pressure within the

aneurysm sac [21, 22]. Type IA endoleaks do not occur in

frozen elephant trunk repair, as the proximal portion of the

stent is sewn to the anastomosis.

MRA using 4D flow analysis has recently been used for

identification and evaluation of endoleaks. 4D flow has

been shown to have a higher sensitivity than CTA for

endoleak detection [23]. In the case of multiple types of

endoleak, 4D flow is able to differentiate between multiple

sources of endoleak [23], and can characterize velocity and

volume of flow into the aneurysm sac [24].

Retrograde Type A dissection (RTAD), a new type A

aortic dissection, is a potentially fatal occurrence after

TEVAR involving the aortic arch or DTA. It can occur

days, weeks, or months after an endovascular procedure

[25]. Although incidence is only about 2.5% of cases,

mortality rate may reach 37.1% [26]. Potential etiologies

for RTAD include procedure-related aortic injury or

device-related pressure on the weakened aortic wall [25].

RTAD is associated with a more proximal placement of a

stent graft (in zones 0–2), oversizing of the stent graft

[25, 27], and is more common when repair is performed for

dissection rather than aneurysm or atherosclerosis [26].

When it occurs, RTAD requires ascending aortic and full

arch repair.

Infection

Infection of graft material may occur at any point in the

post-operative state. Initial findings typically include

abnormal fluid or gas bubbles [16••], but can be difficult to

differentiate from peri-operative inflammation in the

immediate post-operative period. In these cases, delayed

contrast images may be helpful to establish rim enhance-

ment in the case of infected peri-graft fluid or abscess

formation. In advanced cases, pseudoaneurysm or fistula

may form [16••, 20].

Conclusions

Multiple surgical techniques are used in aortic arch repair,

and these can have a variety of imaging appearances.

Familiarity with these surgical techniques is crucial for the

radiologist to understand the expected post-operative

appearance, as well as identify potential complications and

imaging pitfalls that may be encountered on post-operative

evaluation.

Compliance with Ethical Guidelines

Conflict of interest Bang, Green, Reece, DaBreo, and Vargas

declare no conflicts of interest.

Fig. 10 Type IA endoleak after TEVAR. Sagittal oblique image

demonstrates Zone 2 placement of an endovascular stent with contrast

in the peri-graft space (straight arrow) secondary to a type IA

endoleak

32 Page 8 of 10 Curr Radiol Rep (2019) 7:32

123

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